The invention concerns a machine, preferably a honing machine or a drilling machine, for producing non-cylindrical bore surfaces with a machine spindle that is reciprocatingly movable and driven in rotation, to which at least one machining tool is connectable, onto which by feed means a feed movement is transmitted, that, after a deflection, feeds the machining tool radially against the bore surface to be machined and in which the feed movement of the aforementioned feed means is superposed by a feed movement of a means for fine feed.
This concerns a machine for machining bores that under functional conditions locally deform differently by known amounts. The deformations are changes relative to a desired, essentially ideal cylindrical shape. They are produced by tension created by mounting, thermal effects, and dynamic forces (compare K. Löhne, Das GOETZE Zylinderverzugsmesystem und Möglichkeiten zur Reduzierung der Zylinderverzüge (translation: The GOETZE cylinder distortion measuring system and possibilities for reducing cylinder distortions), publication No. 89 36 10 - 12/88 of the Goetze Company; as well as J. Schmid, Optimiertes Honverfahren für Gusseisen-Laufflächen (translation: Optimized honing method for cast iron running surfaces), VDI—Berichte No. 106, pp. 217-235) Such bores are therefore provided with a non-cylindrical bore surface that then assumes the desired cylindrical shape as a result of the deformations generated in the operating state. Bores with bore surfaces machined in this way provide improved operating conditions, for example, reduced friction and higher gas tightness in an internal combustion engine by means of reduced pretension of the piston rings. This method for producing a non-cylindrical bore surface is also referred to as “shape honing”.
FIG. 1 shows in spatial illustration a bore surface machined in this way with a local depression or expansion 11 and a local constriction 22. This shape is the nominal shape that is to be produced by machining and that, when stressed in the operating state, deforms precisely to a cylindrical bore. Such given contours that deviate from a cylindrical shape are defined as inverted deviations from a cylindrical ideal shape and, for example, are determined e.g. by finite element calculations or experimentally.
A method for producing such bore surfaces deviating from the cylindrical shape is disclosed, for example, in EP 1 321 229 A1 and DE 4 007 121 A. Also, Japanese publication JP 2000-291487 A discloses a honing tool with piezoelectric feed elements between the tool body and the honing stones (compare FIGS. 6 and 7, reference numeral 22, as well as paragraphs [35 and 36] of the description). In EP 1 169 154 B1 (=WO 00/62962) a piezoelectric adjusting mechanism is described which is arranged in the tool body between radially opposed cutting edges. In EP 1 790 435 A1 a tool is disclosed with a base feed for complete machining of the bore surface and an additional fine feed for generating shape deviations deviating from a cylindrical shape; the latter is formed by a piezoelectric element arranged between cutter bar and support bar.
For further explaining the object of the invention, reference is being had to FIG. 2: This Figure shows a cross-section of a bore surface machined in such a way that has a depression 11 defined by a shape change ds within an angle dphi. In order to be able to achieve effective functional improvements in bore surfaces of this kind, cylindrical distortions must be generatable by Fourier coefficients up the eighth order. Moreover, with regard to manufacturing technological reasons (reduction of the machining time) the rotary speed of the tool should be selected to be as high as possible. This requires feed dynamics that must be able to thus generate quickly the desired radial adjustment of the cutting means (for example, a honing stone or drill bit cutting edge). As a function of the employed machining method, for example, honing or fine drilling, the radial feed speeds must be defined that result from the required cutting speed that is based on the cutting means.
The object of the present invention resides thus in providing a machine for producing a non-cylindrical bore surface which machine, with respect to its configuration, is simpler and thus less expensive than the prior art machines and has improved feed dynamics.
The aforementioned object is solved in that the means for fine feed is arranged in a tool receiving unit correlated with the machine spindle and is embodied by an axis-parallel acting linear drive, whose actuator acts on a feed rod that is arranged with the machining tool and the means for deflection of the feed movement in a tool unit that is exchangeably connectable to the tool receiving unit. The invention concerns moreover different advantageous further embodiments that are defined in the dependent claims.
According to the invention that concerns honing as well as the aforementioned fine drilling, it is provided for solving the above-mentioned object that the tool receiving unit, that contains the means for fine feed in the form of an axis-parallel directly acting linear drive, is embodied as a non-exchangeable part of the machine spindle and thus of the machine, be it a honing or a fine drilling machine, on which the tool unit—depending on the required tool—is arranged to be exchangeable. The device for fine feed, in this connection preferably the linear drive, therefore, contrary to the prior art, is not to be mounted separately for each tool in the tool unit but is to be provided on the machine only once, namely in the tool receiving unit to be arranged thereat to which different tool units can be connected that must contain the actual machining tools and the deflection means for the feed action but not the—relatively expensive—means for the fine feed action.
In a honing machine that generates by up and down movement with simultaneous rotation of the honing stones in a conventional way a cross-grinding pattern, the observation applies, of course, also analogously to the movement component in the direction of the axis of a bore. This movement component is realized however less quickly than that along the circumference so that the improvement of the feed dynamics that is achieved for the radial feed action leads to an improved result in superposition with the axial component.
In addition to this fine adjustment the known adjustability as a coarse adjustment is still provided.
None of the aforementioned publications shows a tool that by a machine-side tool receptacle, that forms an independent assembly of the machine, with which a dynamic feed action is provided and in which are integrated highly dynamically operating, preferably linearly working, finefeed drives, which temporarily can effect independently from one another the feed movements preferably of several cutting means by means of several axis-parallel feed rods. The tools that are disclosed in the prior publications operate with dynamic fine feed action within the tool with a spacing relative to the cutting means that is as minimal as possible. Therefore, they have only a minimal height and thus also a minimal feed stoke available. Therefore, at such a location it is only possible to mount means for fine feed of a minimal height and therefore with relatively small feed stroke.
According to the invention, one or several axis-parallel acting linear drives can be provided for independent feeding of machining tools or cutting means (honing stones or drill bit cutting edges). The linear drives that are embodied, for example, as piezoelectric linear actuators are activated by electrical control and generate an axial movement of a plunger with a certain force and speed which plunger acts onto the feed rod for radial feed of the cutting means of the machining tools.
For example, it can be realized that for a radial feed stroke of 20 μm within an angle dphi of appr. 25°, a bore diameter of appr. 80 mm, and a rotary speed of 400 l/min. the time for expanding and retrieving a cutting means is appr. 10 ms.
The invention thus provides that the tool unit and the tool receptacle including the linear drive are constructively separated and that the linear drive for the dynamic feed (fine feed) is correlated with the tool receiving unit and thus with the machine or an assembly that is independent of the exchangeable tool unit. On the lower end face of the tool receiving unit the tool unit is exchangeably arranged. The tool unit contains exclusively only components for deflecting the stroke movements generated at the machine into feed movements for the machining tools and optionally the independent feed movements for the guide bars as well as the machining tools and optionally the guide bars themselves.
Supra, it has been stated that the tool receiving unit is provided as a part of the machine. However, this does not preclude that it is realized and mountable as an independent unit.
In the tool body of the tool unit the feed rods are coaxial to the plunger or the plungers of the linear drives of the tool receiving unit. The plungers exert a force that is axis-parallel to the center onto the aligned feed rods. At the end faces of the plungers and the feed rods the feed force is transmitted onto the radially movable machining tools. The end faces are designed such that no shearing forces acting in a normal direction are transmitted. At the lower end of the feed rods wedge surfaces are machined that deflect the axial movement into a radial feed movement.
With the arrangement and design in accordance with the invention of tool receiving unit and tool unit it is possible to produce inverted functional shapes. As a result of the dynamic fine feed of the machining tools, the desired nominal shape can be achieved at high cutting speeds and small shape change segments with great radial shape changes at high precision of a few micrometers.
Positioning of the cutting means with a coarse feed improves the dynamic feed behavior because the fine feed must operate only in the range of the local shape changes. Since the tool receiving unit with the fine feed integrated therein is constructively separated from the tool unit, it is only necessary to arrange in the tool unit exclusively simple mechanically actuated tools without their own feed drives. The tool unit is exchangeable for various machining tasks.
Moreover, the cooling lubricant material has only direct contact with the tool but not with the tool receiving unit in which the means for fine feed are arranged. The linear drives are thus protected from the damaging effect of aggressive liquids.